How Food Cravings Work

You're sitting at your desk at work, mentally absorbed in a beast of a project. Then out of nowhere, something hits your brain like a Mack truck: sushi. You go out for sushi maybe once a month, but all of a sudden you feel as though if you don't get your hands on a pair of chopsticks soon, your body will convulse. You can almost smell the pickled ginger and wasabi wafting from the plate. Your tongue tingles at the memory of the chewy seaweed wrap and the texture of the sticky rice surrounding a cool cucumber filling. Although you were planning a dinner of chicken and veggies, plans have changed. You must have sushi in your belly, stat.

Food cravings don't dictate everything we eat. We are naturally driven to nosh for survival, but cravings go beyond the simple need to quench hunger. In fact, many times, hunger doesn't play a prominent role in where cravings come from since most revolve around the hedonic, or pleasurable, aspects of dining [source: Hill]. Rather, they're a confounding cocktail of body, brain and chemicals that can send us dashing to the grocery store for a tin of anchovies in the middle of the afternoon.

Just about everyone gets food cravings, but gender differences do exist. In general, women are more likely than men to experience food cravings [source: Squires]. Surveys conducted at the Monell Chemical Senses Center found that nearly 100 percent of females and 70 percent of males experienced a food craving in the past year [source: ScienceDaily]. Women in North America and Europe, in particular, salivate for sweets. Men, on the other hand, tend toward the savory side of the menu, digging into barbecue or french fries. For both sexes, the usual foods that lure us in like the Pied Piper of Hamelin are those rich in fat or calories. You'd be hard-pressed to find someone who craves celery sticks without the blue cheese dressing.

Where we live may also dictate what we want. Chocolate, for instance, tops the list of the most widely reported foods craved by American women [source: Yanovski]. On the other hand, Egyptian women go for more flavorful dishes, such as meat-stuffed eggplant [source: McGowan].

Although food cravings are a nearly universal human trait, science has only recently started to unravel their origins. While the meaning of a craving is quite to the point -- "I want a strawberry cupcake with vanilla frosting" -- the interaction of our stomachs, brains and the hormones that elicit these cravings is far more complex. To navigate down this literal candy-land lane, let's kick off where it all begins: in the belly.

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Stomach Hunger

Hunger and cravings are two different sensations. The body regulates the former, while the mind wields greater power over the latter. Hunger serves a more utilitarian purpose, signaling our brains that it's time to eat. To cross that distance between the stomach and brain, the vagus nerve is the communication highway that runs between the noggin and the abdomen.

Our stomach hunger cycle, in a nutshell, begins with a hormone called ghrelin. When our bodies have burned up the food in our stomachs and our blood sugar and insulin levels begin to drop, ghrelin communicates with the hypothalamus in the brain. The hypothalamus, housed in the deep center portion of our brain cavity, regulates our basic body functions such as thirst, sleep and sex drive. Once it receives the message, delivered by ghrelin, that we need to eat something to keep our bodies running, the hypothalamus triggers the release of neuropeptide Y, which stimulates our appetites [source: Wright].

When we recognize that our body wants food and we start to refill it, another process happens to counter that hunger feeling in order to keep us from gorging ourselves. First, the fat tissues expel the hormone leptin. This chemical tells our brains that our bodies are satisfied and we can stop eating. It does so by turning down the production of neuropeptide Y and cranking up levels of proopiomelanocortin, an appetite suppressant, in our bloodstream [source: Wright]. The hypothalamus also monitors our insulin and blood sugar levels to ensure that we've eaten enough to bring those levels back up. Since this process doesn't happen instantaneously, we may feel uncomfortably stuffed after finishing a large meal.

Now that we know how our body responds to the absence of food, what happens when mind takes over matter? If ghrelin isn't telling me that I want a deluxe cheeseburger, what is? Things get a little more complicated when food desires move from the stomach to the brain.

Endocannabinoids and "The Munchies"

One common side effect of marijuana use is linked to a chemical that helps whet our appetites. In addition to a head euphoria, many pot smokers also get cases of "the munchies," leading some to down countless gallons of slushies and economy-sized boxes of pizza rolls. Why the epicurean effect? Mary Jane's active ingredient, tetrahydrocannabinol (THC), binds to CB1 receptors in the brain normally reserved for innate chemicals called endocannabinoids. Endocannabinoids, like neuropeptide Y, tell our brain to rev up our appetites and help us derive pleasure from the food we eat. In addition, these chemicals promote energy storage in our fat tissues, which may be linked to problems with excessive weight. Scientists are closely researching this connection to examine whether endocannabinoids could be controlled with medication to treat obesity.

Mind Hunger and Food Cravings

If we were to compare stomach hunger and mind hunger to different types of telephones, stomach hunger would be a one-line analog phone, and mind hunger would take the form of a high-end cell phone with camera, Internet and MP3-player capabilities. Far more elaborate and complicated, mind hunger isn't entirely necessary for survival. In fact, scientists have largely debunked the theory that food cravings are our bodies' ways of nagging us that we need a specific type of nutrient [source: Pressman and Clemens]. That is, unless you consider macaroni and cheese, chocolate chip cookies and bacon to contain valuable nutrition.

So why do people generally crave items high in fat and calories? The answer lies in the brain. Fatty, sugary foods release chemicals called opioids into our bloodstream [source: Wright]. Opioids bind to receptors in our brains and give us feelings of pleasure and even mild euphoria. In this way, our bodies, at least momentarily, give us a thank you for ingesting that box of truffles or whatnot. This effect from the opioids, contained in the fat of red meat for instance, may be one of the reasons someone might encounter trouble maintaining a vegetarian lifestyle [source: Barnard].

Understanding the parts of the brain that are activated when we crave specific foods provides another clue to this gastronomical mystery. In 2004, participants in a study were asked to think about a favorite food. The participants' resulting fMRI images displayed three primary areas that lit up: the hippocampus, insula and caudate [source: ScienceDaily]. The hippocampus, located in the temporal lobe, filters sensory data and puts it in short-term or long-term memory. Located on either side of the brain, the insula helps control your social emotions by interpreting your physical state [source: Blakeslee]. Then, the caudate nucleus, within the striatum deep in the center of the brain, helps control the dopamine reward system. Dopamine is a feel-good hormone also produced during sex, compulsive gambling and drug activity.

This type of dopamine stimulation and chemical reward that we obtain from fulfilling food cravings has been compared to drug addiction because both behaviors follow similar neural pathways. The pleasure and reward that we derive are simply milder versions of those that drug addicts experience when they get high. Neurologically speaking, that fast food joint isn't much different from a person selling drugs.

Psychological factors can also influence the intensity and nature of our food hankerings. Studies on mood have found that our emotional state normally has a greater impact on cravings than hunger [source: Hill]. Diet influences our levels of the hormone serotonin, which regulates our disposition [source: Pressman and Clemens].

On top of that, our sensory memories of these foods, which elicit that chemical satisfaction, reinforce the cravings. Where do those earliest culinary sensory memories come from? To find the answer, we'll turn back the clock to a time before you could distinguish between a carrot and a cookie.

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How We Acquire Food Cravings

We start figuring out what flavors we like -- and dislike -- during infancy.

Before fast food chains and grocery stores popped up in almost every neighborhood, feeding yourself on a whim wasn't always an option. For that reason, some food psychologists believe that our innate food cravings evolved as a way to ensure that our bodies got enough energy. Granted, much of what we desire is fattening or high in calories, which may translate to obesity today. But back in the time of hunters and gatherers, such energy-dense food would help carry you until your next meal.

We acquire food cravings and the desire for high-calorie nutrition in the womb. At some point during the second trimester, a fetus's senses of taste and smell develop. While in the uterus, fetuses can distinguish between different flavors passed within the amniotic fluid [source: Monell]. Babies are also born with a preference for sweet tastes, which follows many people into adulthood when food cravings occur [source: McGowan]. Hints of a mother's diet also seep into her breast milk. Experiments with babies' tasting capabilities found that if a mother recently ate garlic, the babies drank the breast milk over longer periods of time, as though to figure out the new seasoning [source: McGowan]. In addition, the variety of a mother's diet can predict her child's palate. The more adventurous the mother's diet, the greater likelihood of the child being open to new foods [source: McGowan].

As we age, it's all about the sensory memories that we form in relationship to food. If you think your mom makes the world's best meatloaf, half of your bias likely stems from the positive associations of dinnertime with your family. After all, we only crave the foods that we've had before [source: Squires]. How can you long for crème brûlée if you've never tasted the confection? That point highlights the cultural variations in food cravings, which is why we wouldn't crave a totally foreign dish. As with the brain-reward system discussed earlier, our food cravings are physiological ways to seek out familiar pleasures.

Those familiar pleasures can also have the unwanted consequences of expanding our waistlines. For that reason, many food diets emphasize curbing food cravings and opting for healthier alternatives. But sometimes, resisting the urge isn't the prime alternative.

Managing Food Cravings

Decisions, decisions. If you want to lose weight, give in to that doughnut craving every once in a while, but watch yourself.

Suppressing food cravings can prove a Herculean task. Like trying to get the lyrics of a song out of your head, the longing for loaded baked potato soup can haunt you for hours. But repeatedly succumbing to your every gastronomic desire can negatively affect that dopamine reward system. Just like drug addicts, someone who continually eats chocolate, for instance, raises the threshold of that reward, which means that it gradually takes more and more brownies to regain that initial pleasure [source: Wright].

According to the Centers for Disease Control and Prevention, around one-third of American adults are obese. As that number has risen, more research has gone into managing food cravings (usually high in fat and calories) because studies have shown that it's essential for dropping pounds [source: ScienceDaily]. But doing so has proven trickier than it may initially seem.

Consider the appetite-suppressing hormone leptin, which is produced in fatty tissues. Obese people have greater than average amounts of leptin because they have more fat in their bodies. However, that doesn't translate to a smaller appetite [source: Wright]. Rather, as your Body Mass Index (BMI) increases, so does the frequency of food cravings [source: Squires]. Mentally curbing your cravings can also have unintended results. A 2007 study by Hertfordshire University found that women who tried to quit thinking about eating chocolate ended up eating 50 percent more than those who expressed their desire for the candy [source: BBC].

Limiting your caloric intake through dieting can be a tricky business because your body naturally generates more ghrelin, the hunger hormone, when it thinks you're in danger of starvation. That kick-starts your appetite, which can then open up a Pandora's box of cravings.

Yet all hope isn't lost. Psychologists and nutritionists advise giving in on occasion. The key is limiting the frequency. In a six-month study on the effects of calorie restriction in regard to weight loss, the participants who satisfied their food cravings the least lost the most weight [source: ScienceDaily]. That is to say they didn't quash every craving, but they learned to manage them.

An interesting aspect of dieting and food cravings is that the calorie restriction isn't the sole contributor for a spike in daydreams about doughnuts. Rather, research indicates that anxiety or boredom surrounding dieting is more to blame [source: Hill]. For that reason, experts stress the importance of variety in your diet. There appears to be an inverse relationship between the amount of a certain food you eat and the frequency that you crave it. Spanish women, for example, eat more chocolate than American women and also report fewer cravings for it [source: Pressman and Clemens].

However, women of all sizes may have a bumpier road to travel when dealing with food cravings. Thanks to monthly hormonal shifts and pregnancies, many females are delivered the double punch of mind- and body-related food cravings on a regular basis.

Strange Food Cravings

Does this look like dinner? People with an unnatural affinity for ice may have an eating disorder called pica.

In addition to the mood swings and sluggishness that often accompanies premenstrual syndrome (PMS), a spike in unhealthy food cravings can also occur. According to the Mayo Clinic, a woman's monthly cycle lowers her serotonin levels, which accounts for the mood swings and food cravings. As discussed earlier, mental state correlates to the frequency and strength of cravings, as though the body wants you to stimulate its reward system.

Perhaps the ultimate hormonal surge, pregnancy can send a woman's food cravings into overdrive. Who hasn't heard tired anecdotes about midnight runs to the store for ice cream and pickles? Pregnant women seem more or less expected to have bizarre and overpowering dietary urges such as a newfound adoration of jalapeño peppers or salty Chinese dishes. However, scientists have yet to pinpoint the exact reason behind pregnant women's culinary cravings.

There's a good chance that the odd diets have something to do with women's altered levels of hormones, especially estrogen, during that time. A pregnant woman's sense of taste and smell becomes more acute, leading to strong aversions to certain pungent items such as coffee and cigarettes. Her cravings focus more on intensely sweet, salty or spicy foods. Although some claim that it's the body's way of ensuring that the fetus receives adequate nutrition, this concept doesn't hold much weight since commonly cited pregnancy foods such as pickles and ice cream contain little health value [source: Walker and Humphries].

Among the more strange food cravings is the phenomenon called pica, which is more prevalent among children and pregnant women. Pica, a physiological eating disorder characterized by the desire to eat nonfood items, comes from the Latin word for "magpie," as the bird isn't a very picky eater. Studies of this habit have found that around 20 percent of pregnant women may go through it [source: Bowerman].

What oddball items do they munch on? A study of pregnant women experiencing pica found that about half of them ate ice, a condition called pagophagia [source: Rainville]. Around 15 percent of the other participants ate some form of dirt, clay or cornstarch [source: Rainville]. This practice of dirt eating, or geophagia, is more prevalent in the deep South of the United States and African countries including Kenya and Uganda, where some people may use it as a way to relieve stomach pain or to practice religious customs [source: Bowerman].

This type of pica frequently relates to iron deficiencies in pregnant women, although some researchers think it's related to texture rather than nutrition [source: BBC]. Nevertheless, people with anemia also have a higher likelihood of encountering pica. In the study of pregnant women mentioned above, the participants had lowered levels of hemoglobin, the iron-carrying pigment in red blood cells, when they gave birth [source: Rainville]. Although ice wouldn't augment one's iron stores as dirt might, it may soothe tongue pain that sometimes accompanies the metal's scarcity in the body [source: Bowerman]. Because the habit could wreak havoc on the digestive system, if you suspect you're dealing with pica, you probably want to see a doctor.

If you're jonesing for more information on food cravings, check out the links on the next page.

Pressman, Peter and Clemens, Roger. "Are food cravings the body's way of telling us that we are lacking certain nutrients?" Scientific American. May 23, 2005. (Aug. 7, 2008)http://www.sciam.com/article.cfm?id=are-food-cravings-the-bod